1. Field
The described technology relates generally to an organic electro-luminescence (EL) display device.
2. Description of the Related Technology
Recently, research on organic light emitting diode (OLED) displays using an organic light emitting material as a light emitting element of a display unit has been actively conducted. The organic light emitting diode (OLED) display, unlike a liquid crystal display (LCD), is self-emissive because light is generated by a light-emitting organic electro-luminescence material to display images.
In a conventional transmissive organic light emitting diode (OLED) display, a black display is realized by not emitting light from the organic electro-luminescence element. However, despite the lack of light emission, ambient light from the rear surface is transmitted. Because of the ambient background light it is difficult to display black. As a result, contrast is decreased, and a desired image to be displayed may not be appropriately reproduced.
By a combination of a photochromic layer in the rear surface of the organic light emitting diode (OLED) display, a technique for improving light emission as experience by viewers has been disclosed in Patent Document 1 (Japanese Patent Laid-Open Publication No. 8-78165). Patent Document 1 discloses a technique for improving the light emission from an organic electro-luminescence light emitting element with a colored rear surface when the organic electro-luminescence element is exposed to bright ambient. A photochromic material layer is used on the rear surface of the organic electro-luminescence element. This technique uses a meter installed on an auto dashboard.
However, in the technique disclosed in Patent Document 1, a light blocking state may only be formed on the entire rear surface of the display device. Also, the bright ambient light is required for generating the light blocking state, and the speed of a color change of the photochromic material is too slow for practical applications. Accordingly, because of the color change of the photochromic material and the reaction speed, the above technique may not be used to solve the problem of the black expression in the display device.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the described technology and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.